A damper for a motor vehicle torque transmission device is described, for example, in Applications FR-A-2 947 025 or FR-A-2 988 455 in the name of the Applicant. It allows the transmission of torsional vibrations from the engine output shaft to the gearbox input shaft to be limited.
In known fashion, a damper of this kind has a torque input element, a torque output element, and elastic members mounted between the torque input element and torque output element and acting oppositely to the rotation of the torque input element and torque output element with respect to one another.
When the damper is of the long-travel type (LTD), it comprises several elastic members arranged in groups, the elastic members of one group being arranged in series by means of a phasing member, so that the elastic members of each group deform in phase with one another. The elastic members of a single group can be identical or can have differing characteristics, in particular in terms of length or stiffness.
The phasing member can, during operation, compress the elastic members both in the rotation direction, called the “forward” direction, and in the opposite rotation direction, called the “reverse” direction. The forward direction corresponds to the operating situation in which a torque is transmitted from the torque input element to the torque output element. In certain operating phases, for example when the user abruptly lifts his or her foot off the accelerator, a resistance torque is transmitted from the torque output element to the torque input element, which can cause the phasing member to rotate in the “reverse” direction.
Compression of the elastic members by the phasing member can then cause slippage of the elastic members with respect to the torque input element and/or torque output element. This slippage causes hysteresis effects in the transmission of torque by the damper. Such slippage can also cause premature wear of the elastic members due to friction against the torque input member and/or torque output member.